Preferring peers over customers [was: Do Not Complicate Routing Security with Voodoo Economics]

Patrick W. Gilmore patrick at ianai.net
Sun Sep 4 20:18:33 CDT 2011


On Sep 5, 2011, at 4:03, Randy Bush <randy at psg.com> wrote:

>> Because routing to peers as a policy instead of customer as a matter
>> of policy, outside of corner cases make logical sence.
> 
> welcome to the internet, it does not always make logical sense at first
> glance.
> 
> the myth in academia that customers are always preferred over peers
> comes from about '96 when vaf complained to asp and me (and we moved it
> to nanog for general discussion) that we were not announcing an
> identical prefix list to him at east and west.  the reason turned out to
> be that, on one of the routers, a peer path was shorter in some cases,
> so we had chosen it.  we were perfectly happy with that but vaf was not,
> and he ran the larger network so won the discussion.

The "myth" comes from engineers at large networks saying it is so.

We could also have a small miscommunication here.  For example, if a customer were multi-homed to a peer, and the customer and peer were on the same router, and the customer had prepended a single time (making the AS path equal), by your original statement you would have sent traffic to the peer.  Most people would find that silly.  (And please do not point out customers and peers do not connect to the same router, this is a simple example for illustrative purposes.)

However, the statement you make above says that you preferred the peer because "the path was shorter".  You do not specify if that is IGP distance, AS path length, or some other metric, but it implies if the path were equal, you would prefer the customer - especially since the customer was preferred on the other coast.  So there may be assumptions on one side or the other that are not clear which are causing confusion.


Either way, this seems operationally relevant.

I would like the large networks of the world to state whether they prefer their customer routes over peer routes, and how.  For instance, does $NETWORK prefer customers only when the AS path is the same, or all the time no matter what?

Let's leave out corner cases - e.g. If a customer asks you, via communities or otherwise, to do something different.  This is a poll of default, vanilla configurations.

Please send them to me, or the list, with this subject line.  I shall compile the results and post them somewhere public.  If you cannot speak for your company, I will keep your name private.

Thanx.

-- 
TTFN
patrick





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